1. Field of the Invention
This invention relates to improvements in cylinder locks and particularly to cylinder locks of the type having reciprocating and rotating tumblers.
2. Background Art
Twisting tumbler locks with dual locking mechanisms are embodied in the famous Medeco.RTM. locks manufactured by Medeco Security Locks, Inc. of Salem, Va., and as disclosed, for example, in U.S. Pat. No. Re. 30,198, reissued Jan. 29, 1980, and U.S. Pat. No. 3,722,240 granted Mar. 23, 1973 as well as the millions of Medeco locks made and sold since approximately 1970.
It is highly desirable to have as many key changes as possible for each type of cylinder lock. One of the advantages of the Medeco locks are that they provide a significantly greater number of actual key changes available from that previously known. Although the Medeco locks have been on the market for approximately 16 years, there has been no increase in the number of key changes and it was thought that none could be available.
Another highly desirable feature of a lock is its capability for master keying. One of the principal advantages of the Medeco lock disclosed in U.S. Pat. No. 3,722,240 is its ability to master key. However, it is desired to have even further and greater capability for master-keying.